JP2900569B2 - Optical waveguide device - Google Patents
Optical waveguide deviceInfo
- Publication number
- JP2900569B2 JP2900569B2 JP24243890A JP24243890A JP2900569B2 JP 2900569 B2 JP2900569 B2 JP 2900569B2 JP 24243890 A JP24243890 A JP 24243890A JP 24243890 A JP24243890 A JP 24243890A JP 2900569 B2 JP2900569 B2 JP 2900569B2
- Authority
- JP
- Japan
- Prior art keywords
- optical waveguide
- optical
- buffer layer
- crystal substrate
- waveguide device
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
- G02F1/31—Digital deflection, i.e. optical switching
- G02F1/313—Digital deflection, i.e. optical switching in an optical waveguide structure
- G02F1/3132—Digital deflection, i.e. optical switching in an optical waveguide structure of directional coupler type
Landscapes
- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Integrated Circuits (AREA)
Description
【発明の詳細な説明】 〔産業上の利用分野〕 本発明は、電気光学効果を有する強誘電体結晶基板に
形成された光導波路に係わり、特に光の変調、光路切換
え等に用いられる光導波路デバイスに関する。Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide formed on a ferroelectric crystal substrate having an electro-optic effect, and more particularly to an optical waveguide used for light modulation, optical path switching, and the like. About the device.
〔従来の技術〕 光通信システムの実用化が進むにつれ、さらに大容量
や多機能をもつ高度のシステムが求められており、より
高速の光信号の発生や光伝送路の切換え、交換等の新た
な機能の付加が必要とされている。[Prior art] With the practical application of optical communication systems, advanced systems with larger capacity and more functions are required, and new technologies such as generation of higher-speed optical signals, switching of optical transmission lines, and switching are required. It is necessary to add various functions.
このような要求を満足するために基板表面に形成した
光導波路により構成した導波型の光変調器や光スイッチ
の開発が進められている。これらのデバイスは、小型、
高速、高効率、多素子の集積化が可能という利点があ
る。特にニオブ酸リチウム（LiNbO3）結晶等の強誘電体
材料を用いたものは、光吸収が小さく低損失であるこ
と、大きな電気光学効果を有しているため高効率である
等の特徴があり、従来からも方向性結合型光変調器や光
スイッチ、全反射型光スイッチ等の種々の方式の光導波
路デバイスが報告されている。In order to satisfy such demands, development of a waveguide type optical modulator and an optical switch constituted by an optical waveguide formed on a substrate surface has been advanced. These devices are small,
There are advantages that high speed, high efficiency, and integration of multiple elements are possible. In particular, those using a ferroelectric material such as lithium niobate (LiNbO 3 ) have characteristics such as low light absorption and low loss, and high efficiency due to a large electro-optic effect. Conventionally, various types of optical waveguide devices such as a directional coupling type optical modulator, an optical switch, and a total reflection type optical switch have been reported.
このような光導波路デバイスを実際の光通信システム
に適用する場合、低損失、高速性等の基本的性能と同時
に動作の安定性や長期的信頼性、製造の容易性や安定性
が実用上不可欠である。When such an optical waveguide device is applied to an actual optical communication system, basic performance such as low loss and high speed as well as operational stability, long-term reliability, ease of manufacture and stability are essential for practical use. It is.
第２図（Ａ）、（Ｂ）に従来の光導波路デバイスの一
例として方向性結合型光スイッチの平面図および断面図
を示す。第２図（Ａ）においてＺ軸に垂直に切り出した
ニオブ酸リチウム結晶基板１の表面にチタンを拡散して
屈折率を基板よりも大きくした帯状の光導波路２および
３が形成されており、この光導波路２および３は基板１
の中央部で互いに数μｍ程度まで接近し、方向性結合器
４を構成している。また、方向性結合器４を構成する光
導波路２、３上には、電極による光吸収を防ぐためのバ
ッファ層６を介して電極５が形成されている。第２図
（Ｂ）は方向性結合器４の部分の光導波路２、３に垂直
な断面図を示している。2A and 2B are a plan view and a cross-sectional view of a directional coupling type optical switch as an example of a conventional optical waveguide device. In FIG. 2 (A), strip-shaped optical waveguides 2 and 3 having a refractive index larger than that of the substrate are formed by diffusing titanium on the surface of the lithium niobate crystal substrate 1 cut out perpendicularly to the Z axis. The optical waveguides 2 and 3 are the substrate 1
Are close to each other by about several μm at the center of the directional coupler 4 to constitute the directional coupler 4. On the optical waveguides 2 and 3 constituting the directional coupler 4, an electrode 5 is formed via a buffer layer 6 for preventing light absorption by the electrode. FIG. 2B is a cross-sectional view of a portion of the directional coupler 4 perpendicular to the optical waveguides 2 and 3.
第２図（Ａ）において、光導波路２に入射した入射光
７は方向性結合器４の部分を伝搬するにしたがって近接
した光導波路３へ徐々に光エネルギが移り、方向性結合
器４を通過した後は、光導波路３にほぼ100％エネルギ
が移って出射光８となる。一方、電極５に電圧を印加し
た場合、電気光学効果により電極５下の光導波路２、３
の屈折率が変化し、光導波路２、３を伝搬する導波モー
ドの間に位相速度の不整合が生じ、両者の間の結合状態
が変化し、出射光９が射出することになる。In FIG. 2 (A), the incident light 7 incident on the optical waveguide 2 gradually transfers light energy to the adjacent optical waveguide 3 as it propagates through the directional coupler 4 and passes through the directional coupler 4. After that, almost 100% of the energy is transferred to the optical waveguide 3 to become the emission light 8. On the other hand, when a voltage is applied to the electrode 5, the optical waveguides 2 and 3 below the electrode 5 are formed by the electro-optic effect.
Is changed, a phase velocity mismatch occurs between the waveguide modes propagating in the optical waveguides 2 and 3, the coupling state between the two changes, and the emitted light 9 is emitted.
しかし、従来の光導波路デバイスでは、強誘電体結晶
（例えばニオブ酸リチウム）基板１上に金属（例えばチ
タン）を熱拡散して、光導波路型の方向性結合器４を形
成し、電極５による光の吸収を防ぐためバッファ層６を
形成する際、光導波路２、３での光の閉じ込めを強くす
るために、光導波路２、３よりも屈折率のはるかに小さ
い誘電体として熱膨張係数の小さな二酸化ケイ素（αSi
O2＝４、３×10-6）が用いられている。そのため、基板
１としてニオブ酸リチウムを用いた場合は、この基板１
の熱膨張係数がαLiNbO3＝15、４×10-6のため、バッフ
ァ層６である二酸化ケイ素の熱膨張係数（αSiO2＝４、
３×10-6）との差が大きい。このため、二酸化ケイ素の
成膜時あるいは、成膜後に熱が加わることにより、方向
性結合器４の光導波路部分に歪は加わり、２本の光導波
路２、３を伝搬する導波モードの間に位相速度の不整合
が生じたり、偏光状態が異なったりするようになり、２
本の光導波路２、３間の結合状態が変化することにな
る。そのため、バッファ層６形成後の光導波路デバイス
の光学特性がバッファ層６形成前の特性と大きく異なっ
てしまい、光学特性の安定な光導波路デバイスが得られ
ないという問題があった。However, in a conventional optical waveguide device, a metal (for example, titanium) is thermally diffused on a ferroelectric crystal (for example, lithium niobate) substrate 1 to form an optical waveguide type directional coupler 4, and the electrode 5 is used. When forming the buffer layer 6 to prevent light absorption, in order to increase the confinement of light in the optical waveguides 2 and 3, as a dielectric having a much smaller refractive index than the optical waveguides 2 and 3, Small silicon dioxide (αSi
O 2 = 4, 3 × 10 −6 ) is used. Therefore, when lithium niobate is used as the substrate 1,
Has a thermal expansion coefficient of αLiNbO 3 = 15 and 4 × 10 −6 , the thermal expansion coefficient (αSiO 2 = 4,
3 × 10 −6 ). For this reason, when heat is applied during or after the formation of silicon dioxide, strain is applied to the optical waveguide portion of the directional coupler 4, and during the waveguide mode propagating through the two optical waveguides 2 and 3. Causes a phase velocity mismatch and a different polarization state.
The coupling state between the optical waveguides 2 and 3 changes. Therefore, the optical characteristics of the optical waveguide device after the formation of the buffer layer 6 are significantly different from the characteristics before the formation of the buffer layer 6, and there is a problem that an optical waveguide device with stable optical characteristics cannot be obtained.
本発明の目的は上述した問題に鑑みなされたもので、
安定した光学特性を有する光導波路デバイスを提供する
にある。The object of the present invention has been made in view of the above-mentioned problems,
An object is to provide an optical waveguide device having stable optical characteristics.
〔課題を解決するための手段〕 前記した目的を達成するために、本発明は、電気光学
効果を有する強誘電体結晶基板の表面に形成された光導
波路と、この光導波路の近傍に誘電体から成るバッファ
層を介して設けられかつ電界を制御することによって前
記光導波路の屈折率を変化させる電極とを含んで構成さ
れる光導波路デバイスにおいて、強誘電体結晶基板の裏
面にもバッファ層と同一の誘電体膜をバッファ層と同一
条件で形成したことを特徴とする。Means for Solving the Problems In order to achieve the above object, the present invention provides an optical waveguide formed on the surface of a ferroelectric crystal substrate having an electro-optical effect, and a dielectric near the optical waveguide. An electrode provided through a buffer layer made of and comprising an electrode that changes the refractive index of the optical waveguide by controlling an electric field, the buffer layer also on the back surface of the ferroelectric crystal substrate. The same dielectric film is formed under the same conditions as the buffer layer.
このように本発明によれば、強誘電体結晶基板の裏面
にもバッファ層と同一の誘電体膜をバッファ層と同一条
件で形成したので、バッファ層形成時に強誘電体結晶基
板の表面に生じる強誘電体結晶基板とバッファ層の熱膨
張係数差による応力と同じ大きさの応力が強誘電体結晶
基板の裏面にも生じる。このため、強誘電体結晶基板の
表裏に加わる応力が均衡し、基板を歪ませることがな
い。したがって、強誘電体結晶基板の表面に形成された
光導波路に不均一な歪が加わることがないので、光学特
性の安定した光導波路デバイスが得られる。As described above, according to the present invention, the same dielectric film as the buffer layer is formed on the back surface of the ferroelectric crystal substrate under the same conditions as the buffer layer. A stress having the same magnitude as the stress due to the difference in thermal expansion coefficient between the ferroelectric crystal substrate and the buffer layer also occurs on the back surface of the ferroelectric crystal substrate. For this reason, the stresses applied to the front and back of the ferroelectric crystal substrate are balanced, and the substrate is not distorted. Therefore, the optical waveguide formed on the surface of the ferroelectric crystal substrate is not subjected to non-uniform distortion, so that an optical waveguide device having stable optical characteristics can be obtained.
次に、本発明について図面を参照して説明する。 Next, the present invention will be described with reference to the drawings.
第１図（Ａ）、（Ｂ）は本発明に係る光導波路デバイ
スの一実施例である方向性結合器型光スイッチの平面図
および断面図である。ニオブ酸リチウム（LiNbO3）結晶
基板10の表面にチタン（Ti）を900〜1100℃程度で数時
間熱拡散して、深さ３〜10μｍ程度の光導波路11および
12が形成されており、基板10の中央部で両光導波路11、
12は互いに数μｍまで近接して方向性結合器13を構成し
ている。また、方向性結合器13を構成する光導波路11、
12上には、電極による光吸収を防ぐためバッファ層14を
介して電極15が形成されている。FIGS. 1A and 1B are a plan view and a sectional view of a directional coupler type optical switch which is an embodiment of an optical waveguide device according to the present invention. Titanium (Ti) is thermally diffused on the surface of a lithium niobate (LiNbO 3 ) crystal substrate 10 at about 900 to 1100 ° C. for several hours to form an optical waveguide 11 having a depth of about 3 to 10 μm.
12 are formed, and both optical waveguides 11 and
Numerals 12 constitute a directional coupler 13 close to each other up to several μm. Further, the optical waveguide 11, which constitutes the directional coupler 13,
An electrode 15 is formed on 12 via a buffer layer 14 to prevent light absorption by the electrode.
一方、ニオブ酸リチウム結晶基板10の裏面には、バッ
ファ層14と同一の誘電体膜16がバッファ層14と同一条件
で形成されており、材料としてはニオブ酸リチウム結晶
基板10よりも屈折率の低い二酸化ケイ素（SiO2）が用い
られている。誘電体膜16の成膜は、バッファ層14と同一
成膜条件で行わなければならないので、誘電体膜16とバ
ッファ層14を同時に成膜する手段を用いてもよい。On the other hand, on the back surface of the lithium niobate crystal substrate 10, the same dielectric film 16 as the buffer layer 14 is formed under the same conditions as the buffer layer 14, and as a material, the refractive index is higher than that of the lithium niobate crystal substrate 10. Low silicon dioxide (SiO 2 ) has been used. Since the film formation of the dielectric film 16 must be performed under the same film formation conditions as the buffer layer 14, a means for simultaneously forming the dielectric film 16 and the buffer layer 14 may be used.
今、本方向性結合型光スイッチの動作を説明するに、
光導波路11に入射した入射光17は方向性結合器13の部分
を伝搬するにしたがって近接９した光導波路12へ徐々に
光エネルギが移り、方向性結合器13を通過した後は、光
導波路12にほぼ100％エネルギが移って出射光18とな
る。一方、電極15に電圧を印加した場合、電気光学効果
により電極15下の光導波路11、12の屈折率が変化し、光
導波路11、12を伝搬する導波モードの間に位相速度の不
整合が生じ、両者の間の結合状態が変化し、出射光19が
射出することになる。Now, to explain the operation of the present directional coupling type optical switch,
As the incident light 17 incident on the optical waveguide 11 propagates through the directional coupler 13, the light energy is gradually transferred to the optical waveguide 12 adjacent to the directional coupler 13, and after passing through the directional coupler 13, the light The energy is transferred almost 100% to the output light 18. On the other hand, when a voltage is applied to the electrode 15, the refractive index of the optical waveguides 11, 12 below the electrode 15 changes due to the electro-optic effect, and the phase velocity mismatch between the waveguide modes propagating through the optical waveguides 11, 12 occurs. Occurs, the coupling state between the two changes, and the emitted light 19 is emitted.
以上説明したように本発明によれば、電気光学効果を
有する強誘電体結晶基板表面に形成された光導波路と、
この光導波路の近傍に誘電体から成るバッファ層を介し
て設けられた電極とを含んで構成された光導波路デバイ
スにおいて、強誘電体結晶基板の裏面にもバッファ層と
同一の誘電体膜をバッファ層と同一条件で形成したの
で、バッファ層形成時に強得誘電体結晶基板の表面に生
じる強誘電体結晶基板とバッファ層の熱膨張係数差によ
る応力と同じ大きさの応力が強誘電体結晶基板の裏面に
も生じる。このため、強誘電体結晶基板の表裏に加わる
応力が均衡し、基板を歪ませることがない。したがっ
て、強誘電体結晶基板の表面に形成された光導波路に不
均一な歪が加わることがないので、光学特性の安定した
光導波路デバイスが得られるという効果を奏する。特
に、方向性結合型の光導波路デバイスにおいてその効果
は顕著であり、方向性結合型光スイッチにおいて、歪に
より生ずる分岐比変動を50％から５％以下に低減でき
た。According to the present invention as described above, an optical waveguide formed on the surface of a ferroelectric crystal substrate having an electro-optical effect,
In an optical waveguide device including an electrode provided in the vicinity of the optical waveguide via a buffer layer made of a dielectric, the same dielectric film as the buffer layer is buffered on the back surface of the ferroelectric crystal substrate. Since the ferroelectric crystal substrate is formed under the same conditions as the layer, a stress having the same magnitude as the stress due to the difference in thermal expansion coefficient between the ferroelectric crystal substrate and the buffer layer generated on the surface of the ferroelectric crystal substrate during formation of the buffer layer is generated. Also occurs on the back surface of For this reason, the stresses applied to the front and back of the ferroelectric crystal substrate are balanced, and the substrate is not distorted. Therefore, since an uneven distortion is not applied to the optical waveguide formed on the surface of the ferroelectric crystal substrate, an effect is obtained that an optical waveguide device having stable optical characteristics can be obtained. In particular, the effect is remarkable in the directional coupling type optical waveguide device, and in the directional coupling type optical switch, the branching ratio fluctuation caused by the strain can be reduced from 50% to 5% or less.
第１図（Ａ）、（Ｂ）は本発明に係る光導波路デバイス
の一実施例を示す平面図および断面図、第２図（Ａ）、
（Ｂ）は従来の光導波路デバイスの一例を示す平面図お
よび断面図である。 10……ニオブ酸リチウム結晶基板、11、12……光導波
路、13……方向性結合器、14……バッファ層、15……電
極、16……誘電体膜。1 (A) and 1 (B) are a plan view and a sectional view showing an embodiment of an optical waveguide device according to the present invention, and FIGS.
FIG. 1B is a plan view and a cross-sectional view illustrating an example of a conventional optical waveguide device. 10: Lithium niobate crystal substrate, 11, 12: Optical waveguide, 13: Directional coupler, 14: Buffer layer, 15: Electrode, 16: Dielectric film.
Claims (1)
表面に形成された光導波路と、この光導波路の近傍に誘
電体から成るバッファ層を介して設けられかつ電界を制
御することによって前記光導波路の屈折率を変化させる
電極とを含んで構成される光導波路デバイスにおいて、
前記強誘電体結晶基板の裏面にも前記バッファ層と同一
の誘電体膜をバッファ層と同一条件で形成したことを特
徴とする光導波路デバイス。1. An optical waveguide formed on the surface of a ferroelectric crystal substrate having an electro-optic effect, and a buffer layer made of a dielectric material is provided near the optical waveguide by controlling an electric field. In an optical waveguide device including an electrode that changes the refractive index of the optical waveguide,
An optical waveguide device, wherein the same dielectric film as the buffer layer is formed on the back surface of the ferroelectric crystal substrate under the same conditions as the buffer layer.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24243890A JP2900569B2 (en) | 1990-09-14 | 1990-09-14 | Optical waveguide device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24243890A JP2900569B2 (en) | 1990-09-14 | 1990-09-14 | Optical waveguide device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04122915A JPH04122915A (en) | 1992-04-23 |
| JP2900569B2 true JP2900569B2 (en) | 1999-06-02 |
Family
ID=17089093
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP24243890A Expired - Lifetime JP2900569B2 (en) | 1990-09-14 | 1990-09-14 | Optical waveguide device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2900569B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2720654B2 (en) * | 1991-10-01 | 1998-03-04 | 日本電気株式会社 | Light control device |
-
1990
- 1990-09-14 JP JP24243890A patent/JP2900569B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH04122915A (en) | 1992-04-23 |
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